[Pw_forum] The scf can't converge

[wangweiphysics at yahoo.com.cn]

Dear Paulatto,
Thanks  a lot for your reply!
 
> mixing_beta = 0.05

>this is extremely low, with such a low mixing beta there is no chance the
>code converges in less than 20 iteration!

 In fact, I set mixing_beta = 0.7 (defualt), the scf can't converge within 100 cycles. The troubleshooting in the userguide said that reduce mixing_beta from the default value to 0.3-0.1 or smaller, so I set mixing_beta = 0.2, and 0.05, both are also failed.

> degauss = 0.03

>this is a bit high, if you can afford more kpoints I would suggest to use
>a lower value.

deduce it to 0.01, also failed.
 
I have another queation:
I don't know the difference between atomic position in units of alat and in crystal coordinates. When I use the crystal coordinates, scf can converge easily, but the atom positions in the output file are different from those in the input file. The same atom positins obtain using atomic position in units of alat but can't converge.I am very puzzled!
 
Wang wei,
Southeast University, Nanjing, China
2009.5.17





 


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